The present invention relates to building photographic panoramas of virtual reality and in particular to building spherical environmental maps utilizing some photographs.
In virtual reality systems, synthesis and navigation of virtual environments are usually accomplished using one of the following approaches: 1) three-dimensional modeling and rendering; 2) branching movies; and 3) image-based approach.
Although three-dimensional modeling and rendering is the traditional approach, creating the three-dimensional geometrical entities is a laborious manual process, and special hardware (e.g., a graphic accelerator) may be necessary for rendering, in real time, a highly complex scene.
The branching movies approach is used extensively in the video game industry. Multiple movie segments are connected together to depict spatial paths of selected branch points. This approach is limited in navigability and interaction, and also requires a large amount of storage space to store movies.
For rendering complex scenes, such as real-world scenery, the image-based approach is often considered to be the most reasonable and feasible approach. The image-based approach renders scenes within a fixed time as well as independently of rendering quality and scene complexity.
The image based approach uses an environment map, which is established from a collection of images and characterizes the appearance of a scene when viewed from a particular position. The environment map contains the pixel values used to display the scene. The image environment map is first wrapped onto an object surface having a certain geometry, such as a cube, a sphere, or a cylinder. Afterwards, by locating the viewing position at the geometrical center of the wrapped object, perspective-corrected views of scenes can be reconstructed from the image on the object surface during playback.
There are many types of environment maps for storing data including cubic maps, spherical maps, cylindrical maps, fish-eye or hemispherical maps, and planar maps. Some environments are capable of storing data of omni-directional scenes, while others cannot. Others have used two additional kinds of environment maps in experimental systems: 1) the textured cylinder-like prism, and 2) the texture sphere-like polyhedron (see e.g., W. K. Tsao, “Rendering scenes in the real world for virtual environments using scanned images”, Master Thesis of National Taiwan University, Advisor: Ming Ouhyoung, 1996). Rendering methods for different types of environment maps are described in U.S. Pat. No. 5,396,583; U.S. Pat. No. 5,446,833; U.S. Pat. No. 5,561,756; and U.S. Pat. No. 5,185,667, all of which are incorporated herein by reference.
As for building image-based panoramas, commercially available software (e.g., the QuickTime VR authoring tool suite, from Apple Computer Inc.) can be used to create a seamless panoramic cylindrical image from a set of overlapping pictures. An improved method of a stitching method is described in Hsieh et al., U.S. Ser. No. 08/933,758, filed Sep. 23, 1997, which is incorporated herein by reference. Stitching together photographic images taken from a fish-eye lens is also described in the developer manual of InfinitePictures, Inc. (“SmoothMove Panorama Web Builder”, Developer Manual (Version 2.0) of InfinitePictures, Inc., 1996).
Spherical environment maps are used to store data relating to a surrounding scene. There exists many types of spherical environment maps. Spherical mapping mechanisms are described in U.S. Pat. Nos. 5,359,363, 5,384,588, 5,313,306, and 5,185,667, all of which are incorporated herein by reference. The major advantage of spherical mapping systems is that the environment map is able to provide users with 360 degrees of both horizontal and vertical pannings of views within the mapped sphere. However, a common problem with spherical mapping systems relates to image acquisition. Generally, to acquire the image for a spherical environment map, users usually require special and relatively expensive cameras having fish-eye lenses. Two types of particular interest are the “spherical reflection” map and the “parametric spherical environment” map.
A “spherical reflection” map stores the image of an environment as an orthographic projection on a sphere representing a perfect reflection of the surrounding scene (Zimmermann U.S. Pat. No. 5,185,667). These images with circular shapes are all stored in respective square arrays of pixels. The major disadvantage of spherical reflection maps is that the orientations near the silhouette of the sphere (i.e., the ring-like shape when the sphere is orthographically projected on a sphere) are sampled very sparsely. This makes it more difficult to render the spherical reflection maps for omni-directional and interactive viewers.